- The most important insect pest of Minnesota-grown apples is the apple maggot (Rhagoletis pomonella).
- Appears in early July and is active until September. Peak activity occurs from late July through early August.
- Heavily infested fruit is distorted and inedible, but can be used for cider or animal feed.
- There are nonchemical and chemical options for managing apple maggots.
How to identify apple maggot
The adult fly is 1/4 inch long, smaller than a common housefly.
- It has dark markings on the clear wings and a conspicuous white spot where the thorax joins the abdomen.
- Has three (male) or four (female) white stripes on the abdomen.
Life cycle of apple maggot
Adult apple maggots begin to emerge from the soil starting around July 1, continuing through most of the summer.
- Adult flies often leave and feed outside the orchard, in wooded or brushy areas.
- They return to lay eggs just under the skin of apples.
- Each female fly can lay hundreds of eggs.
- Once eggs hatch, larvae feed for three to four weeks.
- When apples drop to the ground, the larvae transform into pupae in the soil.
- Pupae spend the winter underground, emerging as adults the following summer.
Damage caused by apple maggot
- Apple maggot flies lay eggs in fruit and the fruit becomes pitted and misshapen.
- Each "sting” or hole created by the female fly as she lays an egg, forms a tiny spot or dimple.
- Pulp breaks down, discolors and starts to rot as a result of maggots (larvae) tunneling through the flesh.
- Larvae are rarely seen.
How to protect your trees from apple maggots
- Frequently pick up and remove any apples that fall during the growing season and after harvest.
- Put these apples in the trash or send them to a municipal composting site.
- Do not compost them in your yard.
Removing overripe and rotten apples from around your trees can help reduce apple maggot infestations, but it will not prevent apple maggot flies that come in from other areas.
This method was developed in western Minnesota and should be used after you thin the fruit in early to mid June.
- Enclose each apple in a plastic sandwich bag, either a zipper closure bag or a plain bag closed with staples.
- Snip the bottom corners off each bag with a pair of scissors to leave a small opening for water to run out.
- At harvest, remove the bag.
Bagging fruit takes extra time , however, the apples are protected from apple maggots for the rest of the season.
Bagging is easy to do if you have a small to medium-sized tree that can be managed from the ground or a short ladder.
If you have a tall tree, you may choose to bag only the fruits that are easy to reach, and let the apple maggots have the fruit growing higher up.
Sticky traps capture apple maggot females that attempt to lay eggs on the fruit.
Apple maggot traps are red spheres coated with tanglefoot, a sticky substance that permanently holds insects.
Types of apple traps:
- Wooden or plastic spheres painted red.
- Red plastic spheres designed and sold specifically for this purpose.
- Store-bought large, red, fresh apples coated with tanglefoot. Compost them at the end of the season.
- The Ladd trap is a red sphere and yellow rectangle combination. This trap may be more effective in catching apple maggot flies, even though they can be harder to clean.
Whichever type of trap you choose, the spheres or apples should be at least 3 inches in diameter and bright red.
- Hang up wooden spheres with an eye screw and a wire hook.
- Hang up fresh apples by skewering the apple with a coat hanger and bending the excess wire into a hook.
- Hang scent lures (that smell like the apple fruit) with your traps to make them more attractive to flies.
- Hang one trap per 100 fruit (after thinning) in each tree.
- One or two spheres for small trees and five or more traps for larger trees.
- Place at least one trap on the side of the tree that faces any wooded or brushy area.
- A second trap should hang on the south side of the tree.
If there are apple or hawthorn trees in wooded or landscaped areas nearby, you may want to hang traps in these trees as well, to further reduce apple maggot pressure.
- Hang traps in the trees by the end of June, to catch the apple maggot flies as they first attempt to lay eggs.
- Remove any leaves or fruit touching the traps.
- Check all the traps weekly. Clean off the tanglefoot-coated insects and apply more tanglefoot, as needed .
Kaolin clay can discourage apple maggot flies and other insects from laying eggs in apple plantings. This method is best used with traps and before any pesticide application.
- Apply clay in a visible layer to all surfaces of the tree, leaves and fruit. This acts as a visual and physical repellent to insects.
- Apple maggot females are attracted to the red color of ripening apples, so a grayish-white apple is not attractive to them.
- The layer of clay on fruits repels many insects and they may leave immediately.
- Clay washes off easily even in moderate rain and may not provide enough coverage.
- As fruits expand or clay washes off, reapply.
- A well maintained coating of kaolin clay can protect 90 percent of fruit from apple maggots, but requires more effort than other methods, which can make it less effective.
Check for the presence of apple maggots using sticky red spheres. This will help you decide if you should apply a pesticide.
- Check the trap frequently.
- If you do not use a scent lure, spray for apple maggots as soon as you catch a single adult.
- If you hang a trap with a lure, wait until you have caught a total of five flies.
Effective pesticides available for apple maggot control are esfenvalerate, carbaryl and spinosad.
- Traps need to be cleaned after each spray.
- Reapply tanglefoot if needed and begin checking the traps every day or two as before.
- Spray again and repeat the whole process, as needed.
- You might have to spray for apple maggot three or four times per season.
Fortunately, the number of apple maggot adults reduces as the season progresses and you should be able to stop spraying sometime in August.
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Be sure that the plant you wish to treat is listed on the label of the pesticide you intend to use. And observe the number of days between pesticide application and when you can harvest your crop. Remember, the label is the law.
Reviewed in 2018